1. Field of the Invention
The present invention relates to a perpendicular magnetic recording apparatus.
2. Description of the Related Art
A perpendicular magnetic recording apparatus has a perpendicular double-layered media including a soft underlayer and a perpendicular recording layer, and a magnetic head (single pole head) including a main pole, a return yoke, and an exciting coil, and records data by using magnetic coupling between the magnetic head and the soft underlayer. Since the soft underlayer of the perpendicular double-layered media can be regarded as a part of the magnetic head, it is necessary to stabilize magnetization in the soft underlayer and reduce noise from the soft underlayer.
Magnetization of the soft underlayer is stabilized by using a structure pinning the magnetization of the soft underlayer in one direction in which the soft underlayer is formed on a magnetization pinning layer. For example, a perpendicular magnetic recording media is proposed in which an in-plane hard magnetic layer, an intermediate layer, an in-plane soft magnetic layer, and a perpendicular recording layer are stacked on a substrate, and the intermediate layer is a magnetic layer having saturation magnetization smaller than that of the in-plane hard magnetic layer, a nonmagnetic layer having a thickness smaller than 0.5 nm, or an oxide layer of the in-plane hard magnetic layer (Jpn. Pat. Appln. KOKAI Publication No. 2003-162807). In this perpendicular magnetic recording media, magnetization deviation caused by an external magnetic field is suppressed, and media noise is reduced.
Also, as described above, in the perpendicular magnetic recording apparatus using the perpendicular double-layered media and the single pole head, data is recorded by using the magnetic coupling between the single pole head and the perpendicular double-layered media, i.e., a flow of magnetic flux from the main pole to the return yoke through the soft underlayer. Therefore, miserase of information recorded on the media readily occurs due to remanent magnetization in the main pole. To solve this problem, a method which prevents miserase by reducing the remanent magnetization in the main pole after recording by modifying the shape of the main pole is proposed (Jpn. Pat. Appln. KOKAI Publication No. 2003-317212). However, as the track density (TPI) of the perpendicular recording media increases, the size of the main pole decreases. For example, to realize 200 kTPI, a track width of 0.13 μm or less is necessary. Therefore, the main pole is made into a needle-like shape and becomes magnetically unstable. This makes it difficult to reduce the remanent magnetization and prevent miserase only by modifying the shape of the main pole. In addition, when the track width of the main pole decreases, the field strength of the main pole also decreases. This makes it difficult to maintain the recording quality.
Furthermore, hard disk drives are incorporated in car navigation systems and household electric appliances as well as in personal computers, and are beginning to be used in wide temperature environments accordingly. Especially because a magnetic recording media changes its coercivity in accordance with the use temperature, recording characteristics at room temperature, high temperatures, and low temperatures may also be different. Therefore, hard disk drives are required to be able to write and read data without any problems in wide temperature environments from low temperatures to high temperatures. More specifically, it is necessary to maintain high thermal fluctuation resistance and good fringe characteristics at high temperatures, and maintain high overwrite characteristics and a high S/N ratio at low temperatures.